1. Summary of the Invention
The present invention generally relates to a process and apparatus for welding coated plates, for example, electrically zinc-coated or galvanized steel plates, and more particularly to a process and apparatus for inserting a coating-compatible film at the welding point.
2. Description of the Prior Art
In the car industry, particularly in fabricating undercarriages of vehicles, steel plates are used which are coated in order to provide protection against corrosion. The plates are assembled by resistance spot welding which destroys the coating at the welding points. As a result, protection against corrosion normally provided by the coating is comparatively ineffective at the welding points.
Furthermore, resistance spot welding of coated plates of this kind suffers from numerous difficulties. During formation of the weld, a portion of the protective coating tends to stick to the electrodes. As a result, the electrodes become fouled or clogged so that they must be frequently cleaned, necessitating the shutdown of the installation, thus increasing the overall cost of the operation. The fouling of the electrodes increases their resistance, so that the consumption of power is increased.